Carbon monoxide is usually produced by the catalytic conversion of natural gas, or by the parial oxidation of heavy oils. The synthetic gases produced in these processes are generally separated from the accompanying gases, primarily hydrogen and methane, by means of low temperature separation processes. If considerable quantities of nitrogen are contained in these streams, the nitrogen that remains in these synthetic gases will cause problems in the low temperature separation. When for example, synthetic gases are produced by steam reforming of natural gas, if more than about 2% nitrogen is present in the natural gas, this will result in an undesirable high content of nitrogen in the carbon monoxide product stream.
Higher nitrogen contents most frequently occur in connection with the use of gaseous feedstocks, such as in the use of natural gas, or various refinery gases containing nitrogen. Various methods have thus been employed in order to solve these problems associated with the presence of such amounts of nitrogen. Firstly, instead of subjecting a gaseous feedstock containing nitrogen to a conversion step, e.g. to a steam reforming process, in some cases an oil- or coal gasification process may be used, since as a rule these feedstocks have lower nitrogen levels. However, apart from the fact that by doing so one thus has to use another feedstock, there is also the disadvantage of this not necessarily being the most cost efficient process. Hence, such gasification processes in connection with installations with a production of less than 5000 Nm.sup.3 /h of carbon monoxide are generally considered to be too costly. Another possibility is simply to accept the nitrogen content of the carbon monoxide stream, as long as it is within reasonable limits. While this is, in itself, basically a very simple process, it does have the disadvantage that further processing of the carbon monoxide product becomes very difficult and costly. Yet another possibility is to subject the gaseous feedstock to a nitrogen separation step prior to its conversion. However, this solution requires a second low temperature separation prior to the conversion, along with the necessary preliminary purification steps. This process thus entails considerable additional expense. Finally, it is also possible to separate the carbon monoxide from the gas stream by using a scrubbing process instead of the low temperature separation process. However, the known procedures for such scrubbing processes are quite difficult to perform, particularly since the scrubbing liquids are toxic and corrosive, and since the process requires costly auxiliary equipment, especially for the final purification.
Processes for the production of carbon monoxide from natural gas containing nitrogen, during which nitrogen is separated from the natural gas prior to the conversion, are known, see e.g., "Linde-Reports on Science and Technology," 18, 1973, pages 3 to 6.
The present invention is directed toward the development of a procedure for facilitating the extraction of nitrogen-free carbon monoxide in the simplest possible way.